Active pen

ABSTRACT

An active pen includes an integrated circuit that transmits a downlink signal through a first electrode and receives an uplink signal through a second electrode different from the first electrode. The active pen includes a stop filter inserted between the second electrode and the integrated circuit. The integrated circuit, in operation, performs transmission of the downlink signal and the reception of the uplink signal at the same time.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to an active pen, and particularly, to anactive pen that performs both of transmission and reception.

2. Description of the Related Art

There is a known active pen configured to receive an uplink signaltransmitted by a sensor controller and to transmit a downlink signal tothe sensor controller. Examples of this type of active pen are disclosedin Japanese Patent No. 6059410 (hereinafter referred to as “PatentDocument 1”).

Various active pens are disclosed in Patent Document 1, and a dual-modestylus among them is an active pen supportive of both of a firstcommunication method of two-way communication and a second communicationmethod of one-way communication from the active pen to a sensorcontroller. The dual-mode stylus is configured to operate in the firstcommunication method when the dual-mode stylus receives an uplink signaland operate in the second communication method when the dual-mode stylusdetects a pen touch operation without receiving an uplink signal.

Examples of the communication method of the active pen are disclosed ineach of International Publication No. WO 2017/029836 (hereinafterreferred to as “Patent Document 2”), International Publication No. WO2015/111159 (hereinafter referred to as “Patent Document 3”), U.S. Pat.No. 8,536,471 (hereinafter referred to as “Patent Document 4”), and U.S.Patent Application Publication No. 2012-0105362 (hereinafter referred toas “Patent Document 5”).

The dual-mode stylus described in Patent Document 1 is configured toperform the reception of the uplink signal and the transmission of thedownlink signal in a time-division manner. However, when thetransmission and the reception are performed in the time-divisionmanner, the uplink signal cannot be received while the downlink signalis transmitted (for example, for a period of approximately 4 msec). As aresult, the reception of the uplink signal may be delayed, and the startof the operation in the first communication method may be delayed.Therefore, an improvement is necessary.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an active pen that canprevent a delay in reception of an uplink signal.

A first aspect of the present invention provides an active pen includingfirst and second electrodes provided at different positions, atransmission circuit that uses a booster circuit to cause a change inthe first electrode to thereby transmit a downlink signal, a receptioncircuit that uses the second electrode to detect an uplink signal, and astop filter that prevents a change in a potential of the first electrodefrom affecting a potential of the uplink signal detected by thereception circuit.

A second aspect of the present invention provides an active penincluding a first operation mode for executing a process of detecting anuplink signal reaching a second electrode while a downlink signal istransmitted from a first electrode, and a second operation mode forperforming, in a time-division manner, the transmission of the downlinksignal from the first electrode and the detection of the uplink signalreaching the second electrode, in which the active pen shifts to thesecond operation mode when the uplink signal is detected during anoperation in the first operation mode.

According to the first aspect of the present invention, the active pencan perform the reception of the uplink signal and the transmission ofthe downlink signal at the same time, instead of a time-division manner.Therefore, this can prevent a delay in the reception of the uplinksignal.

According to the second aspect of the present invention, the active penthat has not detected the sensor controller yet so that the transmissiontiming of the uplink signal transmitted by the sensor controller is notrecognized can perform the reception of the uplink signal and thetransmission of the downlink signal at the same time. On the other hand,the active pen that has detected the uplink signal so that thetransmission timing of the uplink signal transmitted by the sensorcontroller is recognized can perform the reception of the uplink signaland the transmission of the downlink signal in a time-division manner.Therefore, the delay in the reception of the uplink signal can beprevented, and once the uplink signal is detected, the uplink signalwith a small amount of noise can be detected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a configuration of a position detection system accordingto an embodiment of the present invention;

FIG. 2 is a state transition diagram of an integrated circuitillustrated in FIG. 1 ;

FIG. 3 is a diagram explaining operations of an active pen and a sensorcontroller in relation to a case in which the sensor controller is asensor controller supportive of a first communication method;

FIG. 4 is a diagram explaining operations of the active pen and thesensor controller in relation to a case in which the sensor controlleris a sensor controller supportive of a second communication method;

FIG. 5 schematically depicts a configuration in the active penillustrated in FIG. 1 ;

FIG. 6 depicts a configuration of a stop filter as a first example of astop filter illustrated in FIG. 5 ;

FIG. 7 depicts results of a simulation of signals run by using theconfiguration of FIG. 6 ;

FIG. 8 depicts a configuration of a reception circuit provided in theintegrated circuit to receive an uplink signal based on an edge signalobtained by extracting only edges of the uplink signal;

FIGS. 9A-9C depict an example of an output signal FO generated by thereception circuit illustrated in FIG. 8 ;

FIG. 10 depicts a configuration of a stop filter as a second example ofthe stop filter illustrated in FIG. 5 ;

FIG. 11 depicts results of a simulation of signals run by using theconfiguration of FIG. 10 ;

FIG. 12 depicts results of a simulation of signals run by using theconfiguration of FIG. 10 ;

FIG. 13 depicts a configuration of a stop filter as a third example ofthe stop filter 26 illustrated in FIG. 5 ;

FIG. 14 depicts results of a simulation of signals run by using theconfiguration of FIG. 13 ;

FIG. 15 depicts a configuration of a stop filter as a fourth example ofthe stop filter illustrated in FIG. 5 ;

FIGS. 16A-16D depict results of a simulation of signals run by using theconfiguration of FIG. 15 ; and

FIG. 17 depicts a configuration of a stop filter as a fifth example ofthe stop filter illustrated in FIG. 5 .

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail with reference to the attached drawings.

FIG. 1 depicts a configuration of a position detection system 1according to an embodiment of the present invention. As illustrated inFIG. 1 , the position detection system 1 includes an active pen 2 and anelectronic device 3 that is a position detection apparatus configured todetect the active pen 2. Examples of the electronic device 3 include atablet computer and a device including a digitizer.

The electronic device 3 includes a touch surface 3 a, a sensor electrodegroup 30 arranged just below the touch surface 3 a, a sensor controller31 connected to the sensor electrode group 30, and a host processor 32that controls each component of the sensor controller 31 including thesecomponents. The sensor controller 31 is an integrated circuit with afunction of communicating with the active pen 2 through the sensorelectrode group 30 to derive the position of the active pen 2 in thetouch surface 3 a, acquiring data from the active pen 2, and supplyingthe derived position and the acquired data to the host processor 32 oneach occasion. The host processor 32 is a central processing unit of theelectronic device 3, and the host processor 32 can execute variousprograms including a drawing application. The drawing application is aprogram with a function of generating digital ink based on the positionand the data supplied from the sensor controller 31, storing the digitalink in a memory of the electronic device 3, and displaying the digitalink on a display.

Capacitance CX is generated between the active pen 2 and the sensorelectrode group 30 when the active pen 2 is near the touch surface 3 a.The sensor controller 31 can exchange charge with (form a capacitivebond with) the active pen 2 through the capacitance CX to therebycommunicate with the active pen 2.

The active pen 2 is an active capacitive stylus (dual stylus) supportiveof both of a first communication method, which is two-way communication,and a second communication method, which is one-way communication fromthe active pen 2 to the sensor controller 31. The first communicationmethod is, for example, a communication method (AES 2.0 system)described in Patent Document 2, and the second communication method is,for example, a communication method (AES 1.0 system) described in PatentDocument 3, a communication method described in Patent Document 4, or acommunication method described in Patent Document 5.

Hereinafter, a signal transmitted from the sensor controller 31 to theactive pen 2 will be referred to as an uplink signal US, and a signaltransmitted from the active pen 2 to the sensor controller 31 will bereferred to as a downlink signal DS. The uplink signal US includes apulse wave (square wave) in which transmission bits are spread by a chipsequence (spreading codes) of a predetermined chip length. The chiplength of an uplink signal US1 (=pulse period of uplink signal US1) is,for example, a time period such as 1 and 2 μsec, and the edge period(rising period or falling period) is, for example, 10 nsec. In AES 2.0,the pulse period of the pulse wave after Manchester coding is 2 μsec. Onthe other hand, the downlink signal DS includes a pulse wave (squarewave), or a signal based on a sine wave (the signal includes asinusoidal signal at a predetermined frequency, and a signal obtained bymodulating the sinusoidal signal). Details of the downlink signal DSwill be described later.

As illustrated in FIG. 1 , the active pen 2 includes a core body 20, apen tip electrode 21 (first electrode), a ring electrode 22 (secondelectrode), a pressure sensor 23, a battery 24, an integrated circuit25, and a stop filter 26. The core body 20 is a member that forms a penaxis of the active pen 2. A front end of the core body 20 provides a pentip of the active pen 2, and a back end is in contact with the pressuresensor 23. The pen tip electrode 21 and the ring electrode 22 areconductors provided at different positions. The pen tip electrode 21 isarranged at the pen tip of the active pen 2, and the ring electrode 22is arranged to surround the core body 20, at a position closer to themiddle portion of the active pen 2 compared to the pen tip electrode 21.

The pressure sensor 23 is a sensor that detects the pressure applied tothe front end of the core body 20. The pressure detected by the pressuresensor 23 is supplied as a pen pressure value to the integrated circuit25. The battery 24 plays a role of supplying power necessary for theoperation of the integrated circuit 25.

The integrated circuit 25 is an integrated circuit including variouscircuits, such as a booster circuit, a transmission circuit, a receptioncircuit, and a processing circuit. The transmission circuit is connectedto the pen tip electrode 21 and the ring electrode 22, and thetransmission circuit plays a role of using the booster circuit to causea change in the pen tip electrode 21 or the ring electrode 22 to therebytransmit the downlink signal DS. The reception circuit is connected tothe ring electrode 22, and the reception circuit plays a role of usingthe ring electrode 22 to perform a detection operation of the uplinksignal US to thereby receive the uplink signal US. The processingcircuit generates a downlink signal DS and executes a process of causingthe transmission circuit to transmit the generated downlink signal DS.In the case of performing the first communication method, the downlinksignal DS is generated based on the uplink signal US received by thereception circuit.

The stop filter 26 is a filter circuit inserted between the ringelectrode 22 and the integrated circuit 25. Although the detailedconfiguration of the stop filter 26 will be described later, the stopfilter 26 is a circuit provided to allow the detection of the uplinksignal US using the ring electrode 22 and the transmission of thedownlink signal DS from the pen tip electrode 21 at the same time.

More specifically, the potential increased by the booster circuit totransmit the downlink signal DS is 18 to 20 V, and the change in thepotential of the pen tip electrode 21 associated with the transmissionof the downlink signal DS also affects the reception circuit. As aresult, the downlink signal DS is superimposed on the potential of theuplink signal US detected by the reception circuit, and it is difficultto detect the uplink signal US at the same time as the transmission ofthe downlink signal DS. The reception strength of the uplink signal USis low when the active pen 2 is in a hover state, in which the ringelectrode 22 is far from the sensor electrode group 30. Therefore, thedetection of the uplink signal US becomes more difficult. The stopfilter 26 plays a role of preventing the change in the potential of thepen tip electrode 21 associated with the transmission of the downlinksignal DS from affecting the potential of the uplink signal US detectedby the reception circuit in the integrated circuit 25 to thereby allowthe detection of the uplink signal US using the ring electrode 22 andthe transmission of the downlink signal DS from the pen tip electrode 21at the same time.

FIG. 2 is a state transition diagram of the integrated circuit 25. Asillustrated in FIG. 2 , the integrated circuit 25 is configured tooperate in one of a discovery mode (first operation mode), a first mode(second operation mode), and a second mode.

The discovery mode is an operation mode of a case in which theintegrated circuit 25 has not detected the electronic device 3 yet. Theintegrated circuit 25 is configured to enter the discovery mode firstwhen the power is turned on. The first and second modes are operationmodes for the integrated circuit 25 to communicate with the sensorcontroller 31 which is supportive of the first and second communicationmethods, respectively.

In the following description, the uplink signal US used in the firstcommunication method will be referred to as an uplink signal US1 in somecases. Among the downlink signals DS used in the first communicationmethod, the signal transmitted from the pen tip electrode 21 will bereferred to as a downlink signal DS1 a in some cases, and the signaltransmitted from the ring electrode 22 will be referred to as a downlinksignal DS1 b in some cases. Among the downlink signals DS used in thesecond communication method, the signal transmitted from the pen tipelectrode 21 will be referred to as a downlink signal DS2 a in somecases, and the signal transmitted from the ring electrode 22 will bereferred to as a downlink signal DS2 b in some cases.

The integrated circuit 25 in the discovery mode uses the ring electrode22 to perform the detection operation of the uplink signal US1 andtransmits the downlink signal DS2 a from the pen tip electrode 21 (stepS1). The detection operation and the transmission are executed at thesame time, instead of in a time-division manner.

The integrated circuit 25 that has detected the uplink signal US1 instep S1 enters the first mode (step S2) and starts the communicationusing the first communication method. Specifically, the integratedcircuit 25 first acquires a transmission and reception schedule of theuplink signal US1 and the downlink signals DS1 a and DS1 b based on thereception timing of the detected uplink signal US1. The integratedcircuit 25 then transmits the downlink signals DS1 a and DS1 b accordingto the transmission and reception schedule (step S10), and once thereception timing of the uplink signal US1 comes (step S11), theintegrated circuit 25 executes the detection operation of the uplinksignal US1 (step S12). The transmission in step S10 and the detectionoperation in step S12 are executed in a time-division manner.

The uplink signal US1 here is a signal modulated with a commandindicating an instruction for the active pen 2. Further, the downlinksignal DS1 a is, for example, a signal including a position signal,which is an unmodulated pulse wave or sine wave, and a data signalmodulated with data included in the active pen 2.

The position signal is used by the sensor controller 31 to derive theposition of the pen tip of the active pen 2. On the other hand, the datasignal is used by the sensor controller 31 to acquire various types ofdata from the active pen 2. In relation to the data signal, theintegrated circuit 25 is configured to acquire the data transmitted bythe data signal according to the command included in the uplink signalUS1 received from the sensor controller 31. Other than the pen pressurevalue described above, the data acquired in this way can include a penID stored in an internal memory of the integrated circuit 25 and switchinformation indicating an on/off state of a switch provided on thesurface of the active pen 2.

The downlink signal DS1 b includes only a position signal that is anunmodulated pulse wave or sine wave. However, the frequency (pulseperiod) of the pulse wave or the sine wave included in the downlinksignal DS1 b is different from the frequency of the downlink signal DS1a. This is for allowing the sensor controller 31, when receivingsignals, to distinguish between the downlink signal DS1 a and thedownlink signal DS1 b. The sensor controller 31 derives the position ofthe ring electrode 22 based on the downlink signal DS1 b, and derivesthe distance between the position of the ring electrode 22 and theposition of the pen tip derived based on the position signal in thedownlink signal DS1 a to thereby acquire the tilt of the active pen 2.

If the integrated circuit 25 detects the uplink signal US1 as a resultof the execution of the detection operation of the uplink signal US1 instep S12, the integrated circuit 25 maintains the first mode and returnsto step S10 to transmit the downlink signals DS1 a and DS1 b (step S13).On the other hand, if the integrated circuit 25 does not detect theuplink signal US1, the integrated circuit 25 exits the first mode toreturn to the discovery mode and continues the process (step S14). Notethat the integrated circuit 25 may be configured to exit the first modeto return to the discovery mode if the integrated circuit 25 does notdetect the uplink signal US1 for a predetermined number of times.

While the integrated circuit 25 is in the discovery mode, the integratedcircuit 25 also monitors the pen pressure value. As a result ofmonitoring, if the integrated circuit 25 detects that the pen pressurevalue is a value larger than 0, the integrated circuit 25 determinesthat the pen tip of the active pen 2 has come in contact with the touchsurface 3 a (pen touch has occurred) and enters the second mode (stepS3) to start the communication of the second communication method.

More specifically, the integrated circuit 25 repeatedly transmits thedownlink signals DS2 a and DS2 b (step S20) while increasing a variableCount one at a time (step S21).

The downlink signals DS2 a and DS2 b here are signals similar to thedownlink signals DS1 a and DS1 b. The sensor controller 31 acquires theposition and the tilt of the active pen 2 and acquires various types ofdata from the active pen 2 based on the downlink signals DS2 a and DS2 bas in the case of the first communication method. However, there is nouplink signal US1, and the sensor controller 31 side cannot request thedata to be transmitted by the active pen 2.

If the variable Count reaches a predetermined value N, the integratedcircuit 25 returns the variable Count to 1 (step S22) and performs pentouch determination (step S23). The pen touch determination is, inshort, an act of determining whether or not the pen pressure value is 0.The integrated circuit 25 determines that the active pen 2 is in the pentouch state if the pen pressure value is not 0 and determines that theactive pen 2 is not in the pen touch state (is in the hover state) ifthe pen pressure value is 0. If the integrated circuit 25 determinesthat the active pen 2 is in the pen touch state, the integrated circuit25 maintains the second mode and returns to step S20 to continuetransmitting the downlink signals DS2 a and DS2 b (step S24). On theother hand, if the integrated circuit 25 determines that the active pen2 is not in the pen touch state, the integrated circuit 25 exits thesecond mode to return to the discovery mode and continues the process(step S25).

FIGS. 3 and 4 are diagrams explaining operations of the active pen 2 andthe sensor controller 31. A sensor controller 31-1 illustrated in FIG. 3represents the sensor controller 31 supportive of the firstcommunication method, and a sensor controller 31-2 illustrated in FIG. 3represents the sensor controller 31 supportive of the secondcommunication method. The operations of the active pen 2 and the sensorcontroller 31 will now be described in detail again with reference toFIGS. 3 and 4 .

Referring first to FIG. 3 , the integrated circuit 25 that has notdiscovered the sensor controller 31 yet is in the discovery mode, andthe integrated circuit 25 also detects the uplink signal US1 reachingthe ring electrode 22 when the integrated circuit 25 transmits thedownlink signal DS2 a from the pen tip electrode 21. Note that “R”illustrated in FIG. 3 represents the detection operation (receptionoperation) of the signal. On the other hand, the sensor controller 31-1transmits the uplink signal US1 in a predetermined period UpIntv, andwhen the sensor controller 31-1 is not transmitting the uplink signalUS1, the sensor controller 31-1 performs the detection operation of thedownlink signals DS 1 a and DS1 b.

Once the active pen 2 enters a receivable area of the uplink signal US1at time t1 (pen-down), the integrated circuit 25 receives the uplinksignal US1 at the following time t2. The integrated circuit 25 that hasreceived the uplink signal US1 in this way enters the first mode andthen repeatedly executes the transmission of the downlink signals DS1 aand DS1 b and the detection operation of the uplink signal US1 in atime-division manner according to the transmission and receptionschedule determined by the reception timing of the uplink signal US1.Although not illustrated in FIG. 3 , the integrated circuit 25 returnsthe operation mode to the discovery mode when the integrated circuit 25does not receive the uplink signal US1 as a result of performing thedetection operation of the uplink signal US1.

Referring to FIG. 4 , the integrated circuit 25 that has detected thatthe pen pressure value has become 0 at time t3 without receiving theuplink signal US1 enters the second mode. The integrated circuit 25repeatedly transmits the downlink signals DS2 a and DS2 b while theintegrated circuit 25 is in the second mode. Once pen-up occurs at timet4, the integrated circuit 25 exits the second mode to return to thediscovery mode at time t5 that is a time period T after time t4. Thetime length of the time period T is determined by the predeterminedvalue N illustrated in FIG. 2 . The integrated circuit 25 continues thesecond mode without returning to the discovery mode when the statereturns to the pen touch state during the time period T.

Next, the stop filter 26 for allowing to execute the detection of theuplink signal US using the ring electrode 22 and the transmission of thedownlink signal DS from the pen tip electrode 21 at the same time willbe described in detail with reference to the drawings.

FIG. 5 schematically depicts a configuration in the active pen 2. Asillustrated in FIG. 5 , the stop filter 26 is inserted in a wireconnecting the ring electrode 22 and the integrated circuit 25.Therefore, the uplink signal US1 reaching the ring electrode 22 issupplied to the integrated circuit 25 through the stop filter 26.

Capacitance CY illustrated in FIG. 5 represents parasitic capacitancegenerated between the pen tip electrode 21 as well as the wireconnecting the pen tip electrode 21 to the integrated circuit 25, andthe ring electrode 22 as well as the wire connecting the ring electrode22 to the integrated circuit 25. Due to the parasitic capacitance CY,the downlink signal DS2 a is superimposed on the uplink signal US1 ifthe downlink signal DS2 a is transmitted from the pen tip electrode 21when the uplink signal US1 is reaching the ring electrode 22. The stopfilter 26 plays a role of removing only the downlink signal DS2 a fromthe uplink signal US1, on which the downlink signal DS2 a issuperimposed, and supplying only the uplink signal US1 to the integratedcircuit 25.

Various configurations can be adopted for the specific configuration ofthe stop filter 26. Therefore, five types of stop filters 26 a to 26 ewill be illustrated, and each stop filter will be described in detail.

FIG. 6 depicts a configuration of the stop filter 26 a as a firstexample of the stop filter 26. FIG. 6 illustrates an example of a casein which the downlink signal DS2 a includes a signal based on a sinewave at a predetermined frequency. Such a downlink signal DS2 a is usedin, for example, AES 1.0, and the predetermined frequency in this caseis 1.8 MHz.

In FIG. 6 and FIGS. 10 and 13 described later, the configurations of theactive pen 2 and the sensor controller 31 are represented by equivalentcircuits. Specifically, an oscillator V1 corresponds to the sensorcontroller 31 and generates the uplink signal US1. An oscillator V2corresponds to the transmission circuit in the integrated circuit 25 andgenerates the downlink signal DS2 a. The capacitance CX represents thecapacitance formed between the ring electrode 22 and the sensorelectrode group 30 (see FIG. 1 ). Capacitance C1 represents capacitanceformed between the ring electrode 22 as well as the wire connecting thering electrode 22 to the integrated circuit 25, and a ground edge. Avoltage Vring corresponds to the signal appearing at the ring electrode22 (the uplink signal US1 on which the downlink signal DS2 a issuperimposed), and a voltage Vfiltout corresponds to an output signal ofthe stop filter 26. Although the circuit in the integrated circuit 25supplied with the voltage Vfiltout is actually the reception circuit,only a series circuit of capacitance C2 and resistance R1 is illustratedin a simplified manner in FIG. 6 and FIGS. 10 and 13 described later. Avoltage Vrxin corresponds to a signal received by the reception circuitprovided with the voltage Vfiltout.

The stop filter 26 a in the example of FIG. 6 includes a band-stopfilter (notch filter) that blocks a specific frequency band includingthe predetermined frequency (carrier frequency of the downlink signalDS2 a). More specifically, as illustrated in FIG. 6 , the stop filter 26a includes a first circuit including two resistance elements with aresistance value R connected in series, in which the connection point ofthe two resistance elements is grounded through a capacitor with acapacity value 2C. The stop filter 26 a also includes a second circuitincluding two capacitors with a capacity value C connected in series, inwhich the connection point of the two capacitors is grounded through aresistance element with a resistance value R/2. The first circuit andthe second circuit are connected in parallel between the ring electrode22 and the integrated circuit 25, and the capacity value C and theresistance value R are set so that a notch frequency 1/2πCR is equal tothe predetermined frequency.

FIG. 7 depicts results of a simulation of signals run by using theconfiguration of FIG. 6 . FIG. 7 illustrates the uplink signal US1, thevoltage Vring, the voltage Vfiltout, and the voltage Vrxin. In thesimulation, the predetermined frequency is 1.8 MHz, and the pulse periodof the uplink signal US1 is 2 μsec. The downlink signal DS2 a, in theform not superimposed on the uplink signal US1, appears in theillustrated part of a period X in the voltage Vring.

As illustrated in FIG. 7 , while the downlink signal DS2 a issuperimposed on the uplink signal US1 in the voltage Vring, the uplinksignal US1 independently appears in the voltages Vfiltout and Vrxin. Itcan be understood from the results that the stop filter 26 a selectivelyblocks the downlink signal DS2 a.

However, as can be understood from FIG. 7 , the uplink signal US1appearing in the voltages Vfiltout and Vrxin is not the original pulsewave but is an edge signal obtained by extracting only the edges of thepulse wave. Therefore, the reception circuit in the integrated circuit25 needs to be able to receive the uplink signal US1 based on the edgesignal. The configuration of the reception circuit configured in thismanner will now be described in detail.

FIG. 8 depicts the configuration of the reception circuit provided inthe integrated circuit 25 to receive the uplink signal US1 based on theedge signal. As illustrated in FIG. 8 , the integrated circuit 25 inthis case includes an amplifier circuit 40, a ΔΣ modulation unit 41, apulse density detection unit 42, a gain control unit 43, an edge matchedfilter 44, a pattern storage unit 45, and an uplink signal restorationunit 46.

The amplifier circuit 40 is a circuit that amplifies the voltageVfiltout output from the stop filter 26 a illustrated in FIG. 6 andsupplies an output signal DO to the ΔΣ modulation unit 41. The amplifiercircuit 40 includes a variable-gain amplifier in which the amplificationfactor can be controlled by the gain control unit 43.

The ΔΣ modulation unit 41 is a functional unit that uses at least tworeference potentials VTP and VTN (VTP=−VTN>0) corresponding to positiveand negative, respectively, to perform a comparison for the outputsignal DO of the amplifier circuit 40 and that executes a feedbackprocess of the comparison result. As illustrated in FIG. 8 , the ΔΣmodulation unit 41 includes a subtraction circuit 41 a, an additioncircuit 41 b, a comparison circuit 41 c, and delay circuits 41 d and 41e.

The comparison circuit 41 c is a circuit that compares an output signalIO of the addition circuit 41 b and the reference potentials VTP andVTN. The comparison circuit 41 c includes three output terminalsincluding an output terminal of a comparison result, a positive-sideoutput terminal (+1), and a negative-side output terminal (−1). A signaloutput from the output terminal of the comparison result among theoutput terminals provides an output signal CO of the ΔΣ modulation unit41.

The operation of the comparison circuit 41 c is as follows. When theoutput signal IO of the addition circuit 41 b is higher than thereference potential VTP, the comparison circuit 41 c outputs the outputsignal CO of +1, sets the potential of the positive-side output terminalto High, and sets the potential of the negative-side output terminal toLow. When the output signal IO of the addition circuit 41 b is lowerthan the reference potential VTN, the comparison circuit 41 c outputsthe output signal CO of −1, sets the potential of the negative-sideoutput terminal to High, and sets the potential of the positive-sideoutput terminal to Low. In other cases, the comparison circuit 41 coutputs the output signal CO of 0 and sets the potentials of thepositive-side output terminal and the negative-side output terminal toLow. As a result of the operation of the comparison circuit 41 c, theoutput signal CO of the comparison circuit 41 c is a ternary pulsesignal with a value of one of +1, 0, and −1.

The comparison circuit 41 c is configured to operate in a period shorterthan the chip length of the chip sequence included in the uplink signalUS1. Therefore, the output signal CO is a pulse signal including aplurality of chips (for example, four chips) for each chip of the chipsequence included in the uplink signal US1.

The delay circuit 41 d is a circuit that multiplies the potential of thepositive-side output terminal of the comparison circuit 41 c by Δ andthen feeds back the signal to the subtraction circuit 41 a afterdelaying the signal by, for example, one clock (one chip of the outputsignal CO). Similarly, the delay circuit 41 e is a circuit thatmultiplies the potential of the negative-side output terminal of thecomparison circuit 41 c by −Δ and then feeds back the signal to thesubtraction circuit 41 a after delaying the signal by, for example, oneclock. It is preferable that the specific value of Δ be a value equal tothe reference potential VTP.

The subtraction circuit 41 a is a circuit that outputs a signal obtainedby subtracting the potential corresponding to the output signals of thedelay circuits 41 d and 41 e from the output signal DO of the amplifiercircuit 40. As a result of the subtraction, the potential level of theinput signal of the addition circuit 41 b drops when the output signalIO of the previous clock is higher than the reference potential VTP, andthe potential level of the input signal of the addition circuit 41 brises when the output signal IO of the previous clock is lower than thereference potential VTN. This can obtain an advantageous effect that thepotential level of the output signal IO of the addition circuit 41 b canbe limited in a certain range.

The addition circuit 41 b is a circuit that outputs a signal obtained byintegrating the output signals of the subtraction circuit 41 a. Theoutput signal IO of the addition circuit 41 b is obtained by adding theoutput signal of the subtraction circuit 41 a to the output signal ofthe addition circuit 41 b of the previous clock.

The pulse density detection unit 42 is a functional unit that detectsthe pulse density of the output signal CO of the ΔΣ modulation unit 41and that notifies the gain control unit 43 of the result. The gaincontrol unit 43 plays a role of controlling the gain of the amplifiercircuit 40 based on the pulse density notified from the pulse densitydetection unit 42 to thereby prevent the output signal CO from beingfixed due to the absolute value of the output signal DO becoming toolarge or too small.

The pattern storage unit 45 includes a storage circuit that stores, as aknown pattern, a ternary chip sequence including a plurality of chipswith values of +1, 0, or 1, for each of a plurality of spreading codes(binary chip sequence) that can be used by the sensor controller 31 totransmit the uplink signal US.

The edge matched filter 44 includes a first-in first-out shift registerthat can store a chip sequence equivalent to the number of chipscorresponding to one spreading code. Every time the edge matched filter44 acquires one chip of the output signal CO of the ΔΣ modulation unit41, the edge matched filter 44 stores the chip in the shift register.Every time the edge matched filter 44 stores one new chip, the edgematched filter 44 calculates a correlation between the chip sequencestored in the shift register at that point and each of a plurality ofknown patterns stored in the pattern storage unit 45. The edge matchedfilter 44 sequentially supplies the results as an output signal FO tothe uplink signal restoration unit 46.

The uplink signal restoration unit 46 determines that the spreading codecorresponding to the pattern used to calculate the output signal FO isdetected when the output signal FO is equal to or greater than apredetermined value. The uplink signal restoration unit 46 then restoresthe uplink signal US1 based on the spreading codes detected one afteranother. The integrated circuit 25 demodulates the uplink signal USrestored in this way to receive the command transmitted by the sensorcontroller 31.

FIGS. 9A-9C depict an example of the output signal FO generated by thereception circuit illustrated in FIG. 8 . FIGS. 9A-9C illustrate a casein which the correlation is calculated by using a pattern correspondingto the chip sequence of the received uplink signal US1. FIG. 9Cillustrates a case in which the voltage Vfiltout is input to thereception circuit. For comparison, FIG. 9A illustrates a case in whichan ideal uplink signal US without noise is input to the receptioncircuit, and FIG. 9B illustrates a case in which the voltage Vring isinput to the reception circuit. It can be understood from the resultsillustrated in FIGS. 9A-9C that by combining the stop filter 26 aillustrated in FIG. 6 and the reception circuit illustrated in FIG. 8 ,the uplink signal US1 can be correctly received as in the case where theideal uplink signal US without noise is input to the reception circuit.

FIG. 10 depicts a configuration of the stop filter 26 b as a secondexample of the stop filter 26. FIG. 10 illustrates an example of a casein which the downlink signal DS2 a includes a pulse wave. However,compared to the uplink signal US1 that is also a pulse wave, the pulseperiod of the downlink signal DS2 a is significantly longer, and thetime length of the edge period is also longer. Specifically, the pulsewave is, for example, 4 μsec to 40 μsec, and the edge period is, forexample, 100 nsec to 5 μsec.

The stop filter 26 b includes a high-pass filter 50 configured to passthe pulse wave (first pulse wave) of the uplink signal US1 and block thepulse wave (second pulse wave) of the downlink signal DS2 a.Specifically, as illustrated in FIG. 10 , it is preferable that thehigh-pass filter 50 include, for example, a CR filter including acapacitor with the capacity value C, in which one end is connected tothe ring electrode 22, and the other end is connected to the integratedcircuit 25, and a resistance element with the resistance value Rconnected between the other end of the capacitor and the ground edge.The capacity value C and the resistance value R are set so that the stopfilter 26 b passes the uplink signal US1 and blocks the downlink signalDS2 a.

FIG. 11 depicts results of a simulation of signals run by using theconfiguration of FIG. 10 . FIG. 11 illustrates the uplink signal US1,the downlink signal DS2 a, the voltage Vring, and the voltage Vfiltout.In the example of FIG. 11 , the pulse period of the uplink signal US1 is2 μsec, and the pulse period of the downlink signal DS2 a is 40 μsec.The time length of an edge period E1 of the uplink signal US1 is 10nsec, and the time length of an edge period E2 of the downlink signalDS2 a is 2 μsec.

As illustrated in FIG. 11 , the downlink signal DS2 a is superimposed onthe uplink signal US1 in the voltage Vring, and the downlink signal DS2a has substantially disappeared in the voltage Vfiltout. It can beunderstood from the results that the stop filter 26 b also selectivelyblocks the downlink signal DS2 a. However, in the example of FIG. 11 ,the uplink signal US1 appearing in the voltage Vfiltout is not theoriginal pulse wave but is an edge signal obtained by extracting onlythe edges of the pulse wave. Therefore, it is preferable that thereception circuit in the integrated circuit 25 be the reception circuitwith the configuration described with reference to FIG. 8 , as in thefirst example.

In the case of using the stop filter 26 b with the configurationillustrated in FIG. 10 , it may be difficult to remove the downlinksignal DS2 a from the voltage Vring if the difference between the timelength of the edge period E2 of the downlink signal DS2 a and the timelength of the edge period E1 of the uplink signal US1 is small. Aspecific example will be described.

FIG. 12 depicts results of a simulation of signals run by using theconfiguration of FIG. 10 as in FIG. 11 . The difference from FIG. 11 isthat the time length of the edge period E2 of the downlink signal DS2 ais 200 nsec. As illustrated in FIG. 12 , edges of the downlink signalDS2 a clearly remain in the voltage Vfiltout in this case.

FIG. 13 depicts a configuration of the stop filter 26 c as a thirdexample of the stop filter 26. The stop filter 26 c can be used to solvethe problem of the stop filter 26 b. The details will now be described.

The stop filter 26 c includes a mute circuit 51 on a back stage of thehigh-pass filter 50 illustrated in FIG. 10 . The mute circuit 51includes a switch element SW and a clock circuit CLK connected betweenthe other end of the capacitor of the high-pass filter 50 and the groundedge. The switch element SW includes a non-inverting input terminal andan inverting input terminal. The switch element SW grounds the outputend of the stop filter 26 c when the difference between the potential ofthe non-inverting input terminal and the potential of the invertinginput terminal is equal to or greater than a predetermined value, andthe switch element SW does not ground the output end otherwise. Further,the clock circuit CLK is configured to output a signal that is High inedge periods of the downlink signal DS2 a and that is Low in otherperiods. The clock circuit CLK supplies the signal to the non-invertinginput terminal of the switch element SW. The operation of the switchelement SW and the clock circuit CLK mutes the output (=voltageVfiltout) of the stop filter 26 c in the edge periods of the downlinksignal DS2 a.

FIG. 14 depicts results of a simulation of signals run by using theconfiguration of FIG. 13 . The waveforms of the uplink signal US1 andthe downlink signal DS2 a are similar to the waveforms in the example ofFIG. 12 . As can be understood by comparing FIG. 14 and FIG. 12 , theedges of the downlink signal DS2 a have disappeared from the voltageVfiltout in the example of FIG. 14 . It can be understood from theresults that the mute circuit 51 plays a role of removing the downlinksignal DS2 a from the voltage Vring.

Here, part of the pulse of the uplink signal US1 may be lost when themute circuit 51 is used. Therefore, as in the first and second examples,it is also preferable in the third example that the reception circuit inthe integrated circuit 25 be the reception circuit with theconfiguration described with reference to FIG. 8 . In this way, thecorrelation calculation by the edge matched filter 44 can restore theuplink signal US1, and the uplink signal US1 can be correctly receivedeven if the pulse of the uplink signal US1 is lost a little due to theaction of the mute circuit 51.

FIG. 15 depicts a configuration of the stop filter 26 d as a fourthexample of the stop filter 26. As illustrated in FIG. 15 , the stopfilter 26 d includes a gain circuit 52 and a differential circuit 53.

The gain circuit 52 is a circuit that outputs the downlink signal DS2 aafter controlling the amplitude of the downlink signal DS2 a. The inputend of the gain circuit 52 is connected to the output end of thetransmission circuit in the integrated circuit 25, and the output end isconnected to the inverting input terminal of the differential circuit53. The gain circuit 52 plays a role of attenuating the amplitude of thedownlink signal DS2 a to a level equivalent to the amplitude of thedownlink signal DS2 a superimposed on the uplink signal US1 through theparasitic capacitance CY.

The differential circuit 53 is a circuit that outputs a signal aftersubtracting the output signal of the gain circuit 52 from the uplinksignal US1 reaching the ring electrode 22. The non-inverting inputterminal of the differential circuit 53 is connected to the ringelectrode 22, and therefore, the uplink signal US1, on which thedownlink signal DS2 a is superimposed through the parasitic capacitanceCY, is input to the non-inverting input terminal of the differentialcircuit 53. As described above, the output signal of the gain circuit 52is the downlink signal DS2 a with the amplitude attenuated to the levelequivalent to the amplitude of the downlink signal DS2 a superimposed onthe uplink signal US1, and therefore, the output signal of thedifferential circuit 53 is the uplink signal US1 on which the downlinksignal DS2 a is not superimposed.

FIGS. 16A-16D depict results of a simulation of signals run by using theconfiguration of FIG. 15 . FIG. 16A illustrates the uplink signal US1generated by the sensor controller 31, and FIGS. 16B to 16D illustratesignals appearing in nodes n1 to n3, respectively, illustrated in FIG.15 . Note that FIGS. 16A-16D illustrate an example, in which both of theuplink signal US1 and the downlink signal DS2 a include pulse waves, andthe pulse period of the downlink signal DS2 a is significantly longerthan the pulse period of the uplink signal US1.

As can be understood from FIGS. 16A-16D, the signal appearing in thenode n1 is a signal in which the uplink signal US1 generated by thesensor controller 31 and the downlink signal DS2 a appearing in the noden2 are superimposed. The signal appearing in the node n3 is a signalwith a waveform similar to the waveform of the original uplink signalUS1 as a result of the removal of the downlink signal DS2 a appearing inthe node n2 from the signal appearing in the node n1. It can beunderstood from the results that the stop filter 26 d plays a role ofremoving the downlink signal DS2 a from the signal reaching the ringelectrode 22.

Although not taken into account in the example of FIGS. 15 and 16 , theuplink signal US1 coming around toward the pen tip electrode 21 throughthe parasitic capacitance CY is superimposed on the actual input of thegain circuit 52. The components of the uplink signal US1 need to beremoved from the downlink signal DS2 a in the stop filter 26 when theinfluence of the superimposition cannot be ignored. In a fifth exampledescribed next, the stop filter 26 that allows the removal will bedescribed.

FIG. 17 depicts a configuration of the stop filter 26 e as a fifthexample of the stop filter 26. As illustrated in FIG. 17 , the stopfilter 26 e includes a finite impulse response (FIR) filter 54, asubtractor 55, and a feedback circuit 56.

The FIR filter 54 is a digital filter configured to extract onlyspecific signal components. The FIR filter 54 in the stop filter 26 eplays a role as a filter circuit that removes the components of theuplink signal US1 from the downlink signal DS2 a output from thetransmission circuit in the integrated circuit 25 and plays a role as again circuit that outputs the downlink signal DS2 a after controllingthe amplitude of the downlink signal DS2 a. Similar to the differentialcircuit 53 illustrated in FIG. 15 , the subtractor 55 is a differentialcircuit that outputs a signal after subtracting the output signal of theFIR filter 54 from the uplink signal US1 reaching the ring electrode 22.

The feedback circuit 56 is a circuit that controls the control amount ofthe amplitude of the downlink signal DS2 a by the FIR filter 54 toreduce the amplitude of the output signal of the subtractor 55 (that is,to reduce the output energy). Specifically, it is preferable to use aleast mean squares (LMS) algorithm to control the value of eachcoefficient included in the transfer function of the FIR filter 54. As aresult of the control by the feedback circuit 56, the signal output fromthe FIR filter 54 is a signal close to a pure downlink signal DS2 a notincluding the components of the uplink signal US1. Therefore, accordingto the stop filter 26 e, the downlink signal DS2 a can be effectivelyremoved from the signal reaching the ring electrode 22 even if theuplink signal US1 is superimposed on the input of the FIR filter 54through the parasitic capacitance CY.

As described above, according to the active pen 2 of the presentembodiments, the stop filter 26 is provided between the ring electrode22 and the integrated circuit 25, and therefore, the reception of theuplink signal US1 and the transmission of the downlink signal DS2 a canbe performed at the same time, instead of in a time-division manner.Therefore, this can prevent a delay in the reception of the uplinksignal US1.

Furthermore, according to the active pen 2 of the present embodiments,the reception of the uplink signal US and the transmission of thedownlink signal DS can be performed at the same time in the stage(discovery mode) in which the sensor controller 31 is not detected yetand the transmission timing of the uplink signal US transmitted by thesensor controller 31 is not recognized. On the other hand, the receptionof the uplink signal US and the transmission of the downlink signal DScan be performed in a time-division manner in the stage (first mode) inwhich the uplink signal US is detected and the transmission timing ofthe uplink signal US transmitted by the sensor controller 31 isrecognized. Therefore, the delay in the reception of the uplink signalUS can be prevented, and once the uplink signal US is detected, theuplink signal US with a small amount of noise can be detected.Furthermore, the downlink signals DS can be transmitted from both of thepen tip electrode 21 and the ring electrode 22, and therefore, the tiltof the active pen 2 can be used.

Although the preferred embodiments of the present invention have beendescribed, the present invention is not limited to the embodiments inany way, and it is obvious that the present invention can be carried outin various modes without departing from the scope of the presentinvention.

For example, although the case of using the uplink signal US1 that is apulse signal has been illustrated and described in the embodiments, thepresent invention can also be advantageously applied to a case of usingthe uplink signal US including a signal based on a sine wave. In a caseof using the stop filter 26 a illustrated in FIG. 6 in this case, theuplink signal US can be a signal based on a sine wave at a frequency notincluded in the specific frequency band blocked by the stop filter 26 a.

Furthermore, although the example of fixing and inserting the stopfilter 26 between the ring electrode 22 and the integrated circuit 25has been described in the embodiments, a first route that goes throughthe stop filter 26, a second route that does not go through the stopfilter 26, and a switch for switching the routes may be provided. Theintegrated circuit 25 may control the switch to validate the first routein the case where the detection operation of the uplink signal US1 andthe transmission of the downlink signal DS2 a are performed at the sametime (discovery mode) and validate the second route in other cases(first and second modes).

Furthermore, although the example of applying the present invention tothe active pen 2 that is a dual-mode stylus has been described in theembodiments, the present invention can be widely applied to the activepen 2 that needs to transmit the downlink signal DS and receive theuplink signal US at the same time.

What is claimed is:
 1. An active pen comprising: an integrated circuitthat transmits a downlink signal through a first electrode and receivesan uplink signal through a second electrode different from the firstelectrode; and a stop filter inserted between the second electrode andthe integrated circuit, wherein the integrated circuit, in operation,performs transmission of the downlink signal and the reception of theuplink signal at the same time.
 2. The active pen according to claim 1,wherein control circuit increases a potential of the first electrodewith a booster circuit.
 3. The active pen according to claim 1, whereinthe stop filter blocks a specific frequency band.
 4. The active penaccording to claim 1, wherein the uplink signal is a first pulse wave,the downlink signal is a second pulse wave in which a time length of anedge period is different from the first pulse wave, and the stop filteris a high-pass filter configured to pass the first pulse wave and blockthe second pulse wave.
 5. The active pen according to claim 1, whereinthe uplink signal and the downlink signal are pulse waves, and the stopfilter includes a high-pass filter configured to pass the pulse waveincluded in the uplink signal and block the pulse wave included in thedownlink signal, and a mute circuit that mutes an input of the uplinksignal to the integrated circuit in an edge period of the downlinksignal.
 6. The active pen according to claim 5, wherein the mute circuitis provided between the high-pass filter and the integrated circuit. 7.The active pen according to claim 5, wherein the integrated circuit isconfigured to receive the uplink signal based on correlationcalculation.
 8. The active pen according to claim 1, wherein the stopfilter includes a gain circuit that outputs the downlink signal aftercontrolling an amplitude of the downlink signal, and a differentialcircuit that outputs a signal after subtracting the output signal of thegain circuit from the uplink signal reaching the second electrode. 9.The active pen according to claim 8, wherein the stop filter furtherincludes a feedback circuit that controls a control amount of theamplitude of the downlink signal by the gain circuit to reduce anamplitude of the output signal of the differential circuit.
 10. Theactive pen according to claim 1, wherein the first electrode is a pentip electrode, and the second electrode is a ring electrode.
 11. Theactive pen according to claim 1, wherein the downlink signal is a signalat a predetermined frequency, and the stop filter is a band-stop filterthat blocks a specific frequency band including the predeterminedfrequency.